The Difference Between Freshwater Pearls and Akoya Pearls

I sell pearls, but most of my friends, family, and acquaintances aren’t particularly interested in pearls.
One of the most common questions I get from them is about the difference between freshwater pearls and Akoya pearls.

Since they’re not really interested in pearls to begin with, I usually give them a simple answer like this:

“They’re both frogs, but it’s kind of like the difference between a bullfrog and a tree frog.”

It’s a pretty rough comparison, but it seems to make sense to people who aren’t into pearls.
For those who already love pearls, I’m sure this is something you’re already familiar with.

The most fundamental difference between the two is where they live.
Freshwater or seawater. That’s the dividing line.

The freshwater mussel used for cultivating freshwater pearls is the Hyriopsis cumingii, and it can only live in freshwater.
Akoya oysters, on the other hand, cannot survive in freshwater environments.

They’re both bivalves, shaped a bit like castanets, but the worlds they live in are entirely different.
Although I’m not into fishing myself, those who enjoy fishing would probably understand this intuitively.
It’s like the difference between fish that live in rivers and lakes, and those that live in the sea.
They’re all fish—but maybe it’s like comparing a carp to a mackerel.
Now that I think about it, we don’t usually compare those two, so it feels a bit odd.

As for their size, the mussels used to produce freshwater pearls can be anywhere from 20 to 30 centimeters wide.
Meanwhile, Akoya oysters are small enough to fit in the palm of your hand—usually less than 10 centimeters.

The Hyriopsis cumingii has a heavy, sturdy feel to it.
Today, freshwater pearl farming is done on a very small scale in Japan,
but I once had the opportunity to visit a freshwater pearl farm at Lake Biwa, the largest lake in Japan.
The mussels there were so big, I thought you could fit several Akoya oysters inside one of them.

While I was there, I asked the farmer about the pearl cultivation process, and learned a few things that surprised me.

In the case of Akoya pearls, we start by inserting a round nucleus and a tiny piece of mantle tissue (about 2mm square) taken from another Akoya oyster.
This mantle tissue is what secretes nacre around the nucleus, eventually forming a pearl.
Usually, only one or two nuclei are inserted into a single Akoya oyster.
In some regions, up to seven small nuclei are inserted to produce so-called “baby pearls.”

Freshwater pearls, on the other hand, are cultivated without a nucleus. Only mantle tissue is inserted.

The procedure for inserting a nucleus into an Akoya oyster is essentially a surgery.
Before the procedure, the oyster is placed in a special bath that relaxes its entire body, causing it to naturally open its shell.
It is then brought to the operating table and gently fixed in place with its shell open.
The technician makes a tiny incision with a surgical knife,
and through that incision, the nucleus is carefully guided into the body,
avoiding any vital organs by inserting it in a V-shaped path.
Then, the mantle tissue is inserted into the same location using a long, slender, spoon-like tool.

It may be hard to picture in words, but this is real surgery.

Now, compare that to how it’s done with freshwater mussels.
Mantle tissue is picked up using a pen-shaped tool and simply inserted into the slightly open shell.
That’s it.

Pick up tissue, insert. Pick up tissue, insert.
This process is repeated rapidly—around 30 to 60 times per mussel.

The first time I saw this, I was shocked by the speed and roughness of it all.
In the end, one freshwater mussel can produce 30 or more pearls, while one Akoya oyster yields just one or two.
Naturally, this leads to lower costs for freshwater pearls, since they can be mass-produced.

So, how about quality?

Of course, there are high- and low-quality pearls in both categories, so we can’t make a simple judgment.
Still, I’ll try to explain the general tendencies.

On average, freshwater pearls tend to have a soft, gentle luster.
Akoya pearls can also have soft luster, but the higher-quality ones tend to exhibit a strong, sharp glow.
It’s relatively rare to see freshwater pearls with that kind of brilliance.

Some say, “Since freshwater pearls are all nacre, their luster tends to be softer.”
But that theory doesn’t quite hold up when you consider nucleated Akoya keshi pearls, which can still have strong luster even without a nucleus.
So ultimately, the difference may come down to the structure of the nacre layer itself.

The nacre is made of alternating layers of aragonite (a form of calcium carbonate) and conchiolin (a protein).
Thousands of these layers stack on top of each other, and light reflecting between them creates the shimmering effect known as “orient.”

In Akoya pearls, the aragonite crystals are extremely fine and neatly aligned,
like rows of bricks in a European cityscape.
Their thinness and density result in sharp, intense reflections—producing that trademark Akoya brilliance.

In contrast, the aragonite crystals in Hyriopsis cumingii tend to be slightly coarser and less orderly.
Because freshwater pearls are nucleated only with tissue, the nacre is thick, but the reflection becomes softer and more diffused.

The result is a pearl with a gentler, more subtle luster.

So if I were to use metaphors again:

• Akoya nacre is like a neat European brick wall.
• Freshwater nacre is like the uneven stone walls of a Japanese castle.

That’s a bit of a stretch, but hopefully you get the idea.

Now, as for color and shape:

Freshwater pearls can come in a wide range of natural colors, including orange, lavender, and pink.
Akoya pearls are mostly white or bluish, though you may occasionally see rare colors like red, yellow, or purple—
but they’re far less common.

In terms of shape, freshwater pearls tend to be baroque, since there’s no nucleus and the nacre can form freely.
Akoya pearls are typically round or near-round, since the nucleus gives them a fixed shape.

So, those are the general differences.

In terms of price, Akoya pearls are more expensive, while freshwater pearls are more affordable.

Freshwater pearls offer a soft, friendly luster and thick nacre due to their nucleus-free structure.
Akoya pearls, by contrast, tend to have a stronger, more elegant shine.

If you want to enjoy pearls casually, freshwater pearls—with their warmth and lower price—can be a lovely choice.
Akoya pearls are a bit more of an investment, but their unique glow is undeniably alluring.

In the end, it’s a matter of personal taste.

Though they’re both bivalves that create pearls, freshwater and Akoya pearls don’t necessarily belong on the same playing field.
Their worlds, methods, and stories are very different.

By the way—this is just between us—but some pearl dealers in Kobe don’t even consider freshwater pearls to be “real pearls.”
I once casually said, “Freshwater pearls are beautiful,” in front of an older dealer, and he got upset:
“Freshwater pearls aren’t real pearls!”

Curious about this, I did some digging.
Apparently, a few decades ago, Chinese freshwater pearls became popular in Japan,
and some unscrupulous dealers sold them as Akoya pearls.
This caused significant losses in the Akoya industry.

Because of that, many older pearl dealers—especially those over 70—still hold a grudge against freshwater pearls.
But in my view, the problem isn’t the pearls. It’s the people.
Blame the sin, not the pearl.

Now, for a little aside.

As I mentioned, I once visited a freshwater pearl farm at Lake Biwa.
For the record, Lake Biwa’s surface area is about 670 square kilometers.
Lake Ontario? About 19,000 square kilometers.
So Lake Biwa is 1/28th the size of Lake Ontario.

To someone from Ontario, Lake Biwa might look like a “nice big puddle.”
But it’s actually a vital freshwater source for cities like Osaka, Kyoto, and Kobe.

Shiga Prefecture, which houses Lake Biwa, often gets teased by its neighboring regions—Kyoto, the elegant capital, and Osaka, the boisterous entertainment hub.
Some people say, “Shiga has nothing but a lake.”
When that happens, Shiga residents have a ready-made response:
“Fine! We’ll cut off your water.”

If you ever meet someone from Shiga, try calling them “the guardians of Kyoto and Osaka’s water.”
They might be surprised—and secretly proud.

…But I digress.

At that pearl farm, I also learned something fascinating about the pen-shaped tool used to insert mantle tissue.
Originally, technicians used chopstick-like tweezers to insert the tissue one by one.
But someone wanted a better method.

So they went to a small parts manufacturer that specializes in pearl tools.
After trial and error, the shop came up with a pen-like tool:
Click the top, and tiny wires pop out, holding the mantle tissue gently—like a miniature claw machine.
I asked, “Why not just use a pin vise?”
They said a pin vise would crush the tissue.

Thanks to this invention, the farm could work faster and more efficiently.

And then there’s the story of how the mussels reproduce.

Akoya oysters are carefully managed in tanks, with temperature and time controlling their spawning.
But Hyriopsis cumingii?
They need catfish.

That’s because their babies—called glochidia—can’t survive on their own.
They can’t swim, and they can’t feed themselves.
So they attach to the gills or fins of fish, and live there like passengers on a train.
They absorb nutrients and drift through the water safely, until they’re strong enough to drop off and live on their own.

When I visited that farm, the first thing I saw inside was a row of tanks full of catfish.
When I asked about them, they told me this story.

They also said they work hard to keep the lake clean—for the catfish.
Without the catfish, there would be no mussels.
And without the mussels, no pearls.

What surprised me most, though, was this:

The man who runs the farm told me he never intended to start freshwater pearl farming.
The government asked him directly, saying they wanted to revitalize Japanese freshwater pearls.
He couldn’t say no.

At first, he received subsidies. But after three years, they were cut off.
By then, he was in too deep to quit.
He’s nearly 70 now, still working with his wife to clean the lake, care for the catfish, and protect the mussels.
They produce lovely pearls—but they can’t compete with cheaper Chinese imports, so selling them is a struggle.
He says it’s hard to even find workers willing to help.

I had some doubts about parts of his story, to be honest.
But then again—maybe that’s just life.

The man keeps doing his best.
The catfish and mussels probably don’t understand why they’re part of this pearl-making journey either.
Still, each one is doing what it’s supposed to do.

And I tried—at least a little—to make peace with that.

Anyway, that was a long aside.

So, that’s the difference between freshwater and Akoya pearls.
This wasn’t about which is better. It was about how each came to be.

Expensive or affordable—if you love something, that alone gives it value.